The present invention relates to a plasma processing device for generating plasma with microwaves and performing a processing such as etching, ashing, film-forming, and film-reformation in manufacturing of a semiconductor device.
In manufacturing of a semiconductor device, a plasma device is frequently used for the formation of an oxide film, crystal growth on a semiconductor layer, and a processing such as etching and ashing. One of such plasma devices is a microwave plasma device capable of generating plasma with stability even at a relatively low pressure. In such a microwave plasma device, microwaves are introduced into a processing vessel through a flat antenna to generate high-density plasma.
Referring to FIG. 11, the above plasma device used for an etching device will be described as one example. The etching device is provided with a cylindrical processing vessel 901 whose side wall and bottom are made of a conductive material such as aluminum, and an insulating plate 902 which is disposed on the upper part of the processing vessel 901 and is made of a material such as quartz. The processing vessel 901 and the insulating plate 902 constitute a closed vessel. The closed vessel is evacuated from air outlets 903, which are formed on the bottom of the processing vessel 901, by an evacuating means (not shown) connected to the air outlets 903 so as to set the inside of the vessel at a prescribed degree of vacuum.
In the enclosed vessel, there are provided a loading base 904 having a substrate to be etched thereon, a supporting base 905 including a cooling means for supporting the loading base 904, and an insulating plate 906. The insulating plate 906 is fixed on the bottom of the processing vessel 901, the supporting base 905 is fixed on the insulating plate 906, and the loading base 904 is fixed on the supporting base 905. The loading base 904 is connected to a matching box 908 via a feeding line 907, and the matching box 908 is connected to a high-frequency power source 909 for bias. The high-frequency power source 909 produces a high frequency such as 13.56 MHz.
Further, desired etching gas is introduced into the processing vessel 901 through an introducing tube 910.
Meanwhile, a flat antenna 921 is placed on the insulating plate 902. The flat antenna 921 is formed as a bottom plate of a waveguide box 922, which is composed of a vessel formed into a short and hollow circular cylinder. A coaxial line 923 is connected to the center of the waveguide box 922 formed into a disk, and an inner conductor 924 placed in the coaxial line 923 is connected to the center of the flat antenna 921 formed into a disk. The other terminals of the coaxial line 923 and the inner conductor 924 are connected to a microwave generator 925. Moreover, the waveguide box 922 includes a conductor 926 with a prescribed permittivity that shortens a wavelength of a microwave to obtain a short in-tube wavelength.
In the above plasma device, firstly, the processing vessel 901 is evacuated to a degree of vacuum such as 0.01 to 10 Pa. And then, etching gas is introduced with a prescribed quantity into the processing vessel 901 from the introducing tube 910. When the etching gas is introduced into the processing vessel 901, a microwave with a frequency such as 2.45 GHz is generated from the microwave generator 925. The microwave is transported to the coaxial line 923 and the waveguide box 922 and is introduced from the flat antenna 921 into the processing vessel 901 via the insulating plate 902, and plasma is generated from the etching gas. Additionally, since bias high-frequency power is applied to the loading base 904, a negative potential is generated on the loading base 904 and ions are drawn out of the produced plasma.
However, the above conventional plasma processing device does not evenly generate plasma. When observing plasma generated in the processing vessel by the above plasma processing device, it is found that a region under the center of the flat antenna has a higher density than the surrounding regions. Therefore, the conventional device is irregular in processing quantity. For example, etching proceeds faster in a region under high-density plasma of a substrate to be processed. The substrate to be processed, a central axis of the loading base for loading the substrate, and a central axis of the flat antenna are generally aligned with a central axis of the cylindrical processing vessel. For this reason, the conventional device has been disadvantageous in that etching proceeds faster at the center of the substrate to be processed.
It is an object of the present invention to provide a plasma processing device for evenly generating plasma by using microwaves in the processing vessel.
In order to achieve the above object, according to the present invention, there is provided a plasma processing device with a loading base for loading a processed substrate placed in an airtight processing vessel, a flat antenna opposed to the loading base, a main coaxial line having one end connected to the flat antenna and the other end short-circuited, a plurality of feeding sections placed on the peripheral surface of the main coaxial line on the same plane perpendicular to an axial direction of the main coaxial line, the feeding sections receiving microwaves shifted in phase along the same circumferential direction, and a microwave supply means for feeding microwaves with the same prescribed frequency to the plurality of feeding sections.
According to the above invention, a high-order mode is excited in microwaves propagated through the main coaxial line.
In the above invention, phase delay of the feeding section adjacent to another in the same circumferential direction is preferably set at natural number-times as much as an angle of the feeding section and the adjacent feeding section, with respect to the intersection of the center line of the main coaxial line and the same plane having the feeding sections thereon. Further, an angle of the feeding section and the adjacent feeding section is preferably set at {360/(M+1)}xc2x0 (M is the number of feeding sections) or more with respect to the intersection of the center line of the main coaxial line and the same plane having the feeding sections thereon. Moreover, the microwave supply means may be provided in the same number as the feeding sections so as to correspond to the feeding sections, and the feeding means may be synchronized with each other to feed microwaves to the corresponding feeding sections.
In the above invention, the feeding sections may be evenly placed on the peripheral surface of the main coaxial line. In the case where the feeding sections are evenly disposed on four parts of the peripheral surface of the main coaxial line, the microwave supply means is preferably constituted by a microwave generation source; a main branch means for branching a microwave outputted from the microwave generation source into two branched microwaves shifted in phase by 180xc2x0; phase delay means for delaying one of the branched microwaves, which are branched by the branch means, in phase by 90xc2x0 from the other branched microwave; and two sub branch means for branching each of the branched microwaves into two supply microwaves shifted in phase by 180xc2x0. One of the branched microwaves is branched by the main branch means, and the other branched microwave is delayed in phase by the phase delay means.
Further, in the above invention, the main coaxial line is short-circuited from the feeding sections at (2Nxe2x88x921)xc2x7xcexg/4 (N is a natural number) where xcexg is a wavelength of the main coaxial line of microwaves supplied by the microwave supply means.